1. Technical Field
This invention relates generally to a method and apparatus for separating valuable material from unwanted material in a mixture, such as a pulp slurry.
2. Background of the Invention
In many industrial processes, flotation is used to separate valuable or desired material from unwanted material. By way of example, in this process the pulp slurry is a mixture of water, valuable material, unwanted material, and chemicals to render the value material to be hydrophobic. The valuable material and unwanted material from an ore are usually ground to a particle size between 45 to 250 microns or roughly 45 to 100 mesh. When the separation takes place in a flotation cell where air bubbles are used to carry the material to the surface of the flotation cell, particles smaller than 400 mesh are usually required. Fine grinding consumes a great amount of electrical energy. In view of this, there is a need in the industry to provide a better way to separate valuable material from unwanted material, e.g., including in such a flotation cell, so as to eliminate problems associated with using air bubbles in such a separation process.
Moreover, By way of example, known techniques for mineral separation include the following:
Other known mineral separation techniques were apparently developed, e.g., to solve the disadvantages associated with the aforementioned flotation separation process, which are based on using magnetic particles, such as magnetite, which is one of the most magnetic of all the naturally occurring minerals on Earth.
As one example, U.S. Pat. No. 4,657,666 discloses a magnetic separation technique for mineral upgrading or concentration that includes steps of:                providing a gangue associated mineral having a hydrophobic surface and in particulate form;        providing a magnetic material in particulate form, silanizing the magnetic material in order to provide a hydrophobic surface;        contacting the gangue associated mineral with the magnetic material in an aqueous liquid, whereby the mineral particles become attached to the surface of the magnetic particles by virtue of interaction between the hydrophobic surfaces of the particles; and        separating the magnetic particles with attached mineral particles from gangue by magnetic means, detaching the mineral particles from the magnetic particles.The magnetic material may include magnetite, haematite, ilmenite, a ferrite or magnetic metal or alloy.        
As a further example, U.S. Pat. No. 4,906,382 discloses a magnetic separation technique for separating particles of a nonmagnetic material from an aqueous mixture that includes steps of:                rendering surfaces of the particles magnetic by contacting with a magnetizing reagent having water containing particles of a magnetic material, each of the magnetic particles having a two layer surfactant coating including an inner layer and an outer layer, the inner layer covering the magnetic particle and being a monomolecular layer of a first water soluble, organic, heteropolar surfactant containing at least 3 carbon atoms and having a functional group on one end which forms a bond with the magnetic particle and a hydrophobic end, and the outer layer coating the inner layer and being monomolecular layer of a second water soluble, organic, heteropolar surfactant containing at least 3 carbon atoms and having a hydrophobic end which is bonded to the hydrophobic end of the first surfactant and a functional group on the other end capable of bonding with the nonmagnetic particles; and        subjecting the aqueous mixture to a magnetic separation to cause the magnetized particles to be separated therefrom.        
However, there are known disadvantages of the aforementioned magnetic separation techniques, e.g., that may include the need for high magnetic fields that are required in order to separate the magnetic particles from the original mixture; the need for complicated, costly equipment required for this purpose; and the need to ensure that the magnetic particle coupled to the ore remains stably attached during the flotation process and can be separated off again after the separation.
U.S. Pat. No. 8,408,395 discloses another known technique for mineral separation that apparently tried to solve the aforementioned disadvantages associated with the aforementioned magnetic separation techniques disclosed in the '666 patent and the '382 patent. For example, the '395 patent discloses a magnetic separation technique for separating a hydrophobic material from a mixture having a hydrophobic material and a hydrophilic material, that includes the steps of:                (A) preparing a slurry or dispersion of the mixture to be treated in a suitable dispersion medium;        (B) contacting the slurry or dispersion from step (A) with a solid, hydrophobic surface to bind the hydrophobic material to be separated from the slurry or the dispersion, the solid hydrophobic surface being an interior wall of a tube, a surface of a plate, a surface of a conveyor belt or an interior wall of a reactor;        (C) removing the solid, hydrophobic surface to which the one hydrophobic material is bound in step (B) from the slurry or dispersion having a hydrophilic material; and        (D) separating the hydrophobic material from the solid, hydrophobic surface,        where the hydrophobic material present in the mixture is hydrophobicized by a substance before carrying out step (B), and also        where the substance is made up of a radical and an anchor group having 1 to 3 reactive groups which interact(s) with the hydrophobic material to be separated off.According to the '395 patentee, the use of a hydrophobicizing substance increases efficiency of separation, citing an example provided in which a glass beaker is coated with hydrophobized magnetite so that a hydrophobic surface is present. In particular, in the example provided, the solid, hydrophobic surface is formed, e.g., as a coating or layer with hydrophobized magnetite (surface-coated with 1-dodecyltrichlorosilane, with 1 nm2 of magnetite surface being laden with about 10-50 molecules of trichlorosilane; diameter of the magnetite particles=10 nm) so that an area of the walls of about 40 cm2 is hydrophobicized. Moreover, the '395 patent discloses that hydrophobic coating or layer has no polar groups, and therefore has a water repellant character. In effect, the '395 patent appears to try to solve problems associated with the aforementioned high magnetic fields, e.g., by removing magnetite from the mixture and incorporating the magnetite into the coating or layer that forms the solid, hydrophobic surface. According to the '395 patent, its mineral separation technique avoids coupling of magnetizable particles to the hydrophobic constituents in the mixture to be separated off, as well as the use of a stream of air. In addition, it is noted the mineral separation technique of the '395 patent is based on the use of magnetite and its associate magnetic forces in order to bind the hydrophobic material to be separated from the slurry or the dispersion to the coating or layer that forms the solid, hydrophobic surface.        